Amine recovery method and apparatus and decarbonation apparatus having same

ABSTRACT

In a decarbonation process for removing carbon dioxide from a carbon dioxide-containing gas with the use of an amine compound-containing absorbing solution, an amine compound accompanying a decarbonated exhaust gas is efficiently recovered in the following manner: A water washing section is constituted in two stages, a first-stage water washing section  64  and a second-stage water washing section  65 . In these water washing sections, recovery of the amine compound accompanying the decarbonated exhaust gas is performed sequentially. Regeneration tower refluxed water is supplied as washing water to the second-stage water washing section  65 . Washing water is withdrawn from the second-stage water washing section  65  and supplied to the first-stage water washing section  64 . Demisters  83, 84  and  85  are provided at outlets of a carbon dioxide absorption section  73 , the first-stage water washing section  64  and the second-stage water washing section  65 . An absorbing solution mist and a washing water mist accompanying the decarbonated exhaust gas are removed by these demisters.

TECHNICAL FIELD

This invention relates to an amine recovery method and apparatus, and adecarbonation apparatus having the amine recovery apparatus.

BACKGROUND ART

In recent years, thermal power equipment and boiler equipment have usedlarge amounts of coal, heavy oil or superheavy oil as fuels. From thepoints of view of air pollution control and Earth environmentpurification, there have been problems in how to decrease the quantitiesand concentrations of emissions of sulfur oxides (mainly sulfurdioxide), nitrogen oxides, and carbon dioxide. Suppression of carbondioxide emission, in particular, has recently been investigated,together with emission control of flon gas and methane gas, from theviewpoint of global warming. For this purpose, methods for removingcarbon dioxide, such as PSA (pressure swing) method, membraneseparation, and absorption by reaction with basic compounds, are understudy.

As an example of a method for removing carbon dioxide with the use ofbasic compounds, Japanese Unexamined Patent Publication No. 1993-184866(related U.S. Pat. No. 5,318,758) proposes a method which performsdecarbonation by using an aqueous solution of an amine compound(hereinafter referred to simply as an amine) as a solution for absorbingcarbon dioxide. In this method, the reaction between carbon dioxide andthe amine compound is an exothermic reaction. Thus, the temperature ofthe absorbing solution in a carbon dioxide absorption section rises toraise the vapor pressure of the amine. That is, the amine-containingabsorbing solution evaporates owing to the temperature increase. As aresult, the amount of the amine compound accompanying a decarbonated gasincreases. Thus, a water washing section is provided in an absorptiontower, and the decarbonated gas and washing water are subjected tovapor-liquid contact in the water washing section, whereby the aminecompound accompanying the decarbonated gas is recovered into a liquidphase.

Concretely, the above-mentioned Japanese Unexamined Patent PublicationNo. 1993-184866 discloses a decarbonation apparatus as shown in FIGS. 2and 3.

In FIG. 2, the reference numeral 1 denotes an absorption tower, 2 acarbon dioxide absorption section, 3 a water washing section, 4 anexhaust gas supply section, 6 is an absorbing solution supply port, 7 anozzle, 8 a liquid reservoir in the water washing section, 9 acirculating pump, 10 a cooler, 11 a nozzle, 12 an absorbing solutiondischarge port, 13 a blower, 14 an exhaust gas supply port, 15 anexhaust gas cooler, 16 a circulating pump, 17 a cooler, 18 a nozzle, and19 a drainage line.

Although a detailed explanation is omitted, a combustion exhaust gassupplied through the exhaust gas supply port 14 is cooled by the coolingtower 15, and then fed to the absorption tower 1. In the carbon dioxideabsorption section 2 of the absorption tower 1, the fed combustionexhaust gas is brought into countercurrent contact with an absorbingsolution supplied through the absorbing solution supply port via thenozzle 7. As a result, carbon dioxide in the combustion exhaust gas isabsorbed and removed by the absorbing solution. The loaded absorbingsolution, which has absorbed carbon dioxide, is sent to a regenerationtower (not shown) through the absorbing solution discharge port 12. Inthe regeneration tower, the loaded absorbing solution is regenerated,and fed again from the absorbing solution supply port 6 to theabsorption tower 1.

On the other hand, the combustion exhaust gas decarbonated in the carbondioxide absorption section (i.e., decarbonated exhaust gas) ascends,accompanied by a large amount of an amine vapor, due to a temperaturerise ascribed to an exothermic reaction between carbon dioxide and anamine compound in the carbon dioxide absorption section 2. The ascendingdecarbonated exhaust gas passes through the liquid reservoir 8, andheads toward the water washing section 3. In the water washing section3, reserved water in the liquid reservoir 8 is transported by thecirculating pump 9, cooled by the cooler 10, and then supplied to thewater washing section 3 as washing water through the nozzle 11. As aresult, this washing water and the decarbonated exhaust gas makecountercurrent contact in the water washing section 3, whereby the aminecompound in the decarbonated exhaust gas is recovered into the liquidphase.

FIG. 3 is characterized by improving the amine recovering ability byutilization of regeneration tower refluxed water. In FIG. 3, thereference numeral 21 denotes an absorption tower, 22 a carbon dioxideabsorption section, 23 a water washing section, 24 an exhaust gas supplyport, 25 an exhaust gas discharge port, 26 an absorbing solution supplyport, 27 a nozzle, 28 a regeneration tower ref luxed withdrawn watersupply port, 29 a nozzle, 30 a cooler, 31 a nozzle, 32 a chargingsection, 33 a circulating pump, 34 a make-up water supply line, 35 anabsorbing solution discharge pump, 36 a heat exchanger, 37 a cooler, 38a regeneration tower, 39 a nozzle, 40 a lower charging section, 41 areboiler, 42 an upper charging section, 43 a refluxed water pump, 44 acarbon dioxide separator, 45 a carbon dioxide discharge line, 46 acooler, 47 a nozzle, 48 a refluxed water supply line, and 49 acombustion gas supply blower.

Although a detailed explanation is omitted, a combustion exhaust gassupplied by the combustion gas supply blower 49 is cooled by the coolingtower 30, and then fed to the absorption tower 21. In the carbon dioxideabsorption section 22 of the absorption tower 21, the fed combustionexhaust gas is brought into countercurrent contact with an absorbingsolution supplied through the absorbing solution supply port 26 via thenozzle 27. As a result, carbon dioxide in the combustion exhaust gas isabsorbed and removed by the absorbing solution. The loaded absorbingsolution, which has absorbed carbon dioxide, is sent to the regenerationtower 38 by the absorbing solution discharge pump 35 through theabsorbing solution discharge port 12. In the regeneration tower 38, theloaded absorbing solution is regenerated, and fed again to theabsorption tower 21 through the absorbing solution supply port 26.

On the other hand, the combustion exhaust gas decarbonated in the carbondioxide absorption section 22 (i.e., decarbonated exhaust gas) ascends,accompanied by a large amount of an amine vapor, owing to a temperaturerise ascribed to an exothermic reaction between carbon dioxide and anamine compound in the carbon dioxide absorption section 22. Theascending decarbonated exhaust gas heads toward the water washingsection 23. In the water washing section 23, part of regeneration towerrefluxed water withdrawn as washing water is supplied to the waterwashing section 23 through the regeneration tower ref luxed withdrawnwater supply port 28 via the nozzle 29. As a result, this washing waterand the decarbonated exhaust gas make countercurrent contact in thewater washing section 23, whereby the amine compound in the decarbonatedexhaust gas is recovered into the liquid phase.

However, according to the above-described conventional decarbonationapparatus shown in FIG. 2, in particular, the water washing section isprovided as one stage. Thus, the concentration of amine recovered by thewashing water is so high that the recovery of amine is insufficient. Asa result, amine accompanies the decarbonated exhaust gas, and isreleased to the outside of the decarbonation process system.Consequently, amine is wasted, causing a concern about an increase inthe operating cost, etc.

The present invention has been accomplished in the light of theforegoing problems. Its object is to provide an amine recovery methodand apparatus, and a decarbonation apparatus equipped with the aminerecovery apparatus, the amine recovery method and apparatus beingcapable of efficiently recovering an amine compound accompanying adecarbonated exhaust gas in a decarbonation process in which carbondioxide is removed from a gas containing carbon dioxide with the use ofan amine compound-containing absorbing solution.

DISCLOSURE OF THE INVENTION

An amine recovery method as a first invention for solving the aboveproblems is an amine recovery method for recovering an amine compoundaccompanying a decarbonated exhaust gas by bringing the decarbonatedexhaust gas into vapor-liquid contact with washing water in a waterwashing section, the decarbonated exhaust gas having had carbon dioxideabsorbed and removed by vapor-liquid contact with an absorbing solutioncontaining the amine compound in a carbon dioxide absorption section,characterized in that

the water washing section is constituted in a plurality of stages, and

recovery of the amine compound accompanying the decarbonated exhaust gasis performed sequentially in the water washing sections in the pluralstages.

Thus, according to the amine recovery method as the first invention, thewater washing section is constituted in a plurality of stages, andrecovery of the amine compound accompanying the decarbonated exhaust gasis performed sequentially in the water washing sections in the pluralstages. Consequently, the amine compound accompanying the decarbonatedexhaust gas can be recovered very efficiently, and the operating costcan be reduced.

An amine recovery method as a second invention is the amine recoverymethod of the first invention, characterized in that

regeneration tower refluxed water is supplied as washing water to thewater washing section.

Thus, according to the amine recovery method of the second invention,the concentration of amine contained in washing water of the waterwashing section is decreased, and the amine recovery ability is furtherenhanced.

An amine recovery method as a third invention is the amine recoverymethod of the first or second invention, characterized in that

washing water is withdrawn from the water washing section in thesucceeding stage and supplied to the water washing section in thepreceding stage.

Thus, according to the amine recovery method of the third invention, theconcentration of amine contained in washing water of the water washingsection in the preceding stage is decreased to enhance the aminerecovery ability in the water washing section in the preceding stage. Inaccordance with this advantage, the concentration of amine contained inwashing water of the water washing section in the succeeding stage isalso further decreased to further enhance the amine recovery ability asa whole.

An amine recovery method as a fourth invention is the amine recoverymethod of the first, second or third invention, characterized in that

demisters are provided at outlets of the carbon dioxide absorptionsection and the water washing sections in the respective stages, and

an absorbing solution mist and a washing water mist accompanying thedecarbonated exhaust gas are removed by the demisters.

Thus, according to the amine recovery method of the fourth invention, itcan be prevented that part of the absorbing solution mist fed to thecarbon dioxide absorption section and part of the washing water mist fedto the water washing sections in the respective stages are released tothe outside of the system together with the decarbonated exhaust gas,causing losses in water and amine compound.

An amine recovery apparatus as a fifth invention is an amine recoveryapparatus for recovering an amine compound accompanying a decarbonatedexhaust gas by bringing the decarbonated exhaust gas into vapor-liquidcontact with washing water in a water washing section, the decarbonatedexhaust gas having had carbon dioxide absorbed and removed byvapor-liquid contact with an absorbing solution containing the aminecompound in a carbon dioxide absorption section, characterized in that

the water washing section is constituted in a plurality of stages, and

recovery of the amine compound accompanying the decarbonated exhaust gasis performed sequentially in the water washing sections in the pluralstages.

Thus, according to the amine recovery apparatus of the fifth invention,the water washing section is constituted in a plurality of stages, andrecovery of the amine compound accompanying the decarbonated exhaust gasis performed sequentially in the water washing sections in the pluralstages. Consequently, the amine compound accompanying the decarbonatedexhaust gas can be recovered very efficiently, and the operating costcan be reduced.

An amine recovery apparatus as a sixth invention is the amine recoveryapparatus of the fifth invention, characterized in that

regeneration tower refluxed water is supplied as washing water to thewater washing section.

Thus, according to the amine recovery apparatus of the sixth invention,the concentration of amine contained in washing water of the waterwashing section is decreased, and the amine recovery ability is furtherenhanced.

An amine recovery apparatus as a seventh invention is the amine recoveryapparatus of the fifth or sixth invention, characterized in that

washing water is withdrawn from the water washing section in thesucceeding stage and supplied to the water washing section in thepreceding stage.

Thus, according to the amine recovery apparatus of the seventhinvention, the concentration of amine contained in washing water of thewater washing section in the preceding stage is decreased to enhance theamine recovery ability in the water washing section in the precedingstage. In accordance with this advantage, the concentration of aminecontained in washing water of the water washing section in thesucceeding stage is also further decreased to further enhance the aminerecovery ability as a whole.

An amine recovery apparatus as an eighth invention is the amine recoveryapparatus of the fifth, sixth or seventh invention, characterized inthat

demisters are provided at outlets of the carbon dioxide absorptionsection and the water washing sections in the respective stages, and

an absorbing solution mist and a washing water mist accompanying thedecarbonated exhaust gas are removed by the demisters.

Thus, according to the amine recovery apparatus of the eighth invention,it can be prevented that part of the absorbing solution mist fed to thecarbon dioxide absorption section and part of the washing water mist fedto the water washing sections in the respective stages are released tothe outside of the system together with the decarbonated exhaust gas,causing losses in water and amine compound.

A decarbonation apparatus as a ninth invention is characterized byhaving the amine recovery apparatus of the fifth, sixth, seventh oreighth invention in an absorption tower.

Thus, the decarbonation apparatus of the ninth invention has the aminerecovery apparatus of the fifteenth, sixth, seventh or eighth inventionin an absorption tower. Hence, the decarbonation apparatus is anapparatus with a high ability to recover the amine compound andinvolving a low operating cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration drawing showing a main portion of adecarbonation apparatus according to an embodiment of the presentinvention.

FIG. 2 is a configuration drawing showing a main portion of aconventional decarbonation apparatus.

FIG. 3 is a configuration drawing showing a main portion of aconventional decarbonation apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described in detailbased on the accompanying drawings.

FIG. 1 is a configuration drawing showing a main portion of adecarbonation apparatus according to the embodiment of the presentinvention. As shown in FIG. 1, the decarbonation apparatus of thepresent embodiment has an absorption tower 61, a regeneration tower 62,and a cooling tower 63.

Although details will be described later, the decarbonation apparatus ofthe present embodiment is characterized in that a water washing sectionof the absorption tower 61 has a two-stage structure, i.e., afirst-stage water washing section 64 and a second-stage water washingsection 65; that washing water of the second-stage water washing section65 is withdrawn and supplied to the first-stage water washing section64; that regeneration tower ref luxed water is supplied as washing waterto the second-stage water washing section; and that demisters 83, 84 and85 are installed at outlets of a carbon dioxide absorption section 73,the first-stage water washing section 64 and the second-stage waterwashing section 65.

In detail, a combustion exhaust gas generated in thermal power equipmentor boiler equipment is supplied to the cooling tower 63 via an exhaustgas supply line 66. Water is stored at the bottom 67 of the coolingtower 63. This water is scooped up by a circulating pump 68, cooled by aheat exchanger 69, and then supplied to a charging section 71 through anozzle 70. As a result, the combustion exhaust gas is cooled in thecharging section 71 upon countercurrent contact with cooling waterdiffused from the nozzle 70. Then, the combustion exhaust gas issupplied through an exhaust gas supply line 72 to the carbon dioxideabsorption section 73 provided in a lower portion of the absorptiontower 61.

The combustion exhaust gas supplied to the absorption tower 61 ascendswithin the absorption tower as indicated by dotted arrows in thedrawing. On the other hand, a regenerated absorbing solution (an aqueoussolution of an amine compound) reserved at the bottom 76 of theregeneration tower 62 is transported by an absorbing solution supplypump 77 provided in an absorbing solution supply line 74. Thetransported regeneration absorbing solution is cooled by a heatexchanger 78 and a heat exchanger 79, and then supplied to the carbondioxide absorption section 73 through a nozzle 75 provided at the outletof the carbon dioxide absorption section 73. As a result, the combustionexhaust gas and the absorbing solution make vapor-liquid contact(countercurrent contact) in the carbon dioxide absorption section 73.Thus, carbon dioxide contained in the combustion exhaust gas is absorbedinto the absorbing solution and removed thereby.

Examples of the amine compound contained in the absorbing solution arealcoholic hydroxyl group-containing primary amines such asmonoethanolamine and 2-amino-2-methyl-1-propanol, alcoholic hydroxylgroup-containing secondary amines such as diethanolamine and2-methylaminoethanol, alcoholic hydroxyl group-containing tertiaryamines such as triethanolamine and N-methyldiethanolamine,polyethylenepolyamines such as ethylenediamine, triethylenediamine anddiethylenetriamine, cyclic amines such as piperazines, piperidines andpyrrolidines, polyamines such as xylylenediamine, amino acids such asmethylaminocarboxylic acid, and mixtures of them. Any of these amines isused usually as 10 to 70% by weight of an aqueous solution. To theabsorbing solution, carbon dioxide absorption promoters or corrosioninhibitors may be added, and methanol, polyethylene glycol and sulfolanemay be added as other media.

The loaded absorbing solution, which has absorbed carbon dioxide, flowsdownward, and is stored at the bottom 80 of the absorption tower. Then,the stored solution is discharged by an absorbing solution dischargepump 87 provided in an absorbing solution discharge line 86, and isheated upon heat exchange with the regenerated absorbing solution in theheat exchanger 78. Then, the heated solution is diffused from a nozzle89 provided at the outlet of a lower charging section 88 of theregeneration tower 62, flows down the lower charging section 88, and isstored at the bottom 76 of the regeneration tower.

The loaded absorbing solution stored at the bottom 76 of theregeneration tower is heated to, for example, about 120° C. by feedsteam in a reboiler 90. As a result, carbon dioxide in the loadedabsorbing solution is released to regenerate the absorbing solution.This regenerated absorbing solution is stored at the bottom 76 of theregeneration tower, and supplied again to the carbon dioxide absorptionsection 73 of the absorption tower 61. That is, the absorbing solutionis used in a circulated manner, and need not be discharged to theoutside or supplied from the outside, unless any loss occurs. On theother hand, the carbon dioxide released ascends as indicated by dottedarrows in the drawing, passes through the lower charging section 88 andan upper charging section 91, and is discharged to the outside of theregeneration tower through a carbon dioxide discharge line 93 at the top111 of the regeneration tower.

Since the carbon dioxide at this time contains moisture, it is cooled bya condenser (cooler) 94 provided in the carbon dioxide discharge line 93to condense moisture contained in the carbon dioxide. The resultingcondensate and carbon dioxide are separated by a carbon dioxideseparator 95. High purity carbon dioxide separated from the condensateis released to the outside of the decarbonation process system(hereinafter referred to simply as the outside of the system) through acarbon dioxide release line 96, and is utilized in a subsequent step ordisposed of. The condensate is transported by a circulating pump 96, andpart of it is withdrawn toward a regeneration tower refluxed watersupply line 97. This regeneration tower refluxed withdrawn water iscooled by a heat exchanger 98, and then supplied as washing water to thetop of the second-stage water washing section 65 through a nozzle 99provided at the outlet of the second-stage water washing section 65.This regeneration tower refluxed withdrawn water has a very low amineconcentration. The remainder of the condensate is ref luxed to theregeneration tower 62. That is, it is supplied to the top of the uppercharging section 91 through a nozzle 92 via a reflux line 100, floweddownward, and reserved at the bottom 76 of the regeneration tower.

On the other hand, the combustion exhaust gas deprived of carbon dioxide(i.e., decarbonated exhaust gas) in the carbon dioxide absorptionsection 73 of the absorption tower 61 passes through the demister 83provided at the outlet of the carbon dioxide absorption section 73, andflows into the first-stage water washing section 64. At this time, thedecarbonated exhaust gas is accompanied by a large amount of an aminevapor. That is, the temperature rises because of the exothermic reactionbetween carbon dioxide and the amine compound in the carbon dioxideabsorption section 73, so that a large amount of the absorbing solutionevaporates, ascending together with the decarbonated exhaust gas. Themoisture accompanying the decarbonated exhaust gas at this time becomesa supply source for washing water in the water washing section to bedescribed later. The temperature of the decarbonated exhaust gas,flowing into the first-stage water washing section 64, is about 50 to80° C., for example.

The demister 83 removes a mist of the absorbing solution accompanyingthe decarbonated exhaust gas. That is, the absorbing solution isdiffused from the nozzle 75 as a mist, and part of this absorbingsolution mist accompanies the decarbonated exhaust gas and ascends. Ifthe absorbing solution mist is released, unchanged, to the outside ofthe absorption tower along with the decarbonated exhaust gas, there willbe a loss of the amine compound. Thus, the demister 83 is provided atthe outlet of the carbon dioxide absorption section to remove theabsorbing solution mist accompanying the decarbonated exhaust gas. Themoisture (absorbing solution) removed by the demister 83 flows downward,and is reserved at the bottom 80 of the absorption tower.

In the first-stage water washing section 64, reserved water in a liquidreservoir 81 in the first-stage water washing section 64 is transportedby a circulating pump 102 provided in a circulation line 101. Thetransported water is cooled by a heat exchanger 103, and then suppliedas washing water to the top of the first-stage water washing section 64through a nozzle 104 provided at the outlet of the first-stage waterwashing section 64. As a result, the washing water and the decarbonatedexhaust gas make countercurrent contact in the first-stage water washingsection 64. Consequently, the temperature of the decarbonated exhaustgas lowers, whereupon a water vapor accompanying the decarbonatedexhaust gas condenses. Also, the amine compound accompanying thedecarbonated exhaust gas is recovered. The resulting condensate and thediffused washing water flow downward, and are stored in the liquidreservoir 81.

The reserved water in the liquid reservoir 81 is maintained at aconstant water level. That is, when the reserved water in the liquidreservoir 81 increases and reaches more than the constant water level,the reserved water is overflowed to the bottom 80 of the absorptiontower via a reserved water discharge line 105. The reserved water in theliquid reservoir 81 may be transported to the bottom 80 of theabsorption tower by a pump.

Most of the amine compound accompanying the decarbonated exhaust gas isrecovered in the first-stage water washing section 64. At this time, theamine concentration of the reserved water (washing water) in the liquidreservoir 81 is high. Thus, the amine vapor pressure becomes so highbecause of vapor-liquid equilibrium that the amine concentration in thedecarbonated exhaust gas cannot be decreased any further. That is, thesingle-stage water washing section alone cannot fully decrease the amineconcentration in the decarbonated exhaust gas. In the presentembodiment, therefore, the water washing section has a two-stagestructure, the first-stage water washing section 64 and the second-stagewater washing section 65. The decarbonated exhaust gas having aminerecovered in the first-stage water washing section 64 passes through thedemister 84 provided at the outlet of the first-stage water washingsection 64, and flows to the second-stage water washing section 65.

The demister 84 removes a mist of the washing water accompanying thedecarbonated exhaust gas. That is, the washing water is diffused fromthe nozzle 104 as a mist, and part of this washing water mistaccompanies the decarbonated exhaust gas and ascends. If the washingwater mist is released, unchanged, to the outside of the absorptiontower along with the decarbonated exhaust gas, there will be a loss ofthe amine compound. Thus, the demister 84 is provided at the outlet ofthe first-stage water washing section to remove the washing water mistaccompanying the decarbonated exhaust gas. The moisture (washing water)removed by the demister 83 flows downward, and is reserved in the liquidreservoir 81.

In the second-stage water washing section 65, reserved water in a liquidreservoir 82 in the second-stage water washing section 65 is transportedby a circulating pump 107 provided in a circulation line 106. Thetransported water is cooled by the heat exchanger 98, and then suppliedas washing water to the top of the second-stage water washing section 65through the nozzle 99 provided at the outlet of the second-stage waterwashing section 65. The regeneration tower refluxed withdrawn watersupplied from the regeneration tower also merges into this washingwater. As a result, the combined washing water and the decarbonatedexhaust gas make countercurrent contact in the second-stage waterwashing section 65. Consequently, the amine compound accompanying thedecarbonated exhaust gas is recovered.

Most of the amine compound accompanying the decarbonated exhaust gas isrecovered in the first-stage water washing section 64. In thesecond-stage water washing section 65, therefore, the amineconcentration of the liquid reservoir 82, namely, the concentration ofthe amine contained in the washing water supplied through the nozzle 99,is kept very low. Thus, in the second-stage water washing section 65,the amine concentration in the decarbonated exhaust gas is fullydecreased because of vapor-liquid equilibrium. That is, in thesecond-stage water washing section 65, the amine compound can be furtherrecovered from the decarbonated exhaust gas released from thefirst-stage water washing section 64, so that the amine concentration inthe decarbonated exhaust gas can be fully decreased.

Furthermore, washing water in the second-stage water washing section 65is withdrawn and supplied to the first-stage water washing section 64.Concretely, part of the reserved water (washing water) in the liquidreservoir 82 is withdrawn, and supplied to the liquid reservoir 81 ofthe first-stage water washing section 64. That is, the reserved water inthe liquid reservoir 82 is maintained at a constant water level. Whenthe reserved water in the liquid reservoir 82 increases and reacheshigher than the constant water level, the reserved water is overflowedto the liquid reservoir 81 via a reserved water discharge line 108.However, this mode is not restrictive, and the reserved water (washingwater) in the liquid reservoir 82 may be supplied to the liquidreservoir 81 by a pump.

The decarbonated exhaust gas having amine recovered in the second-stagewater washing section 65 passes through the demister 85 provided at theoutlet of the second-stage water washing section 65, and is released tothe outside of the system through a gas release line 110 at the top 109of the absorption tower. The amine concentration in the decarbonatedexhaust gas released to the outside of the system is a very low value.

The demister 85 removes a mist of the washing water accompanying thedecarbonated exhaust gas. That is, the washing water is diffused fromthe nozzle 99 as a mist, and part of this washing water mist accompaniesthe decarbonated exhaust gas and ascends. If the washing water mist isreleased, unchanged, to the outside of the absorption tower along withthe decarbonated exhaust gas, there will be a loss of the aminecompound. Thus, the demister 85 is provided at the outlet of thesecond-stage water washing section to remove the washing water mistaccompanying the decarbonated exhaust gas. The moisture removed by thedemister 85 flows downward, and is reserved in the liquid reservoir 82.

The cooling ability of the heat exchanger 98, for example, is adjustedso that the amount of moisture brought from the exhaust gas supply line72 into the absorption tower together with the combustion exhaust gas,and the amount of moisture brought through the gas release line 110 tothe outside of the absorption tower together with the combustion exhaustgas are made equal to maintain water balance. This measure makes waterdischarge to the outside or water supply from the outside unnecessaryunless there is a loss.

Moreover, the cooling ability of the heat exchanger 98 and so on areadjusted so that the temperature of the decarbonated exhaust gasreleased through the gas release line 110 is equal to the temperature atthe inlet of the second-stage water washing section 65. In this case,the temperatures at the outlet and the inlet of the second-stage waterwashing section 65 are equal. Thus, steam in the decarbonated exhaustgas in the second-stage water washing section 65 does not condense, andonly the amount of water corresponding to the regeneration tower refluxed withdrawn water overflows and is fed to the liquid reservoir 81 ofthe first-stage water washing section 64. This mode is not necessarilyrestrictive, and the outlet temperature of the second-stage waterwashing section 65 may be adjusted to be lower than its inlettemperature to cause condensation of moisture in the decarbonatedexhaust gas even in the second-stage water washing section 65. Throughthis means, the amount of the resulting condensate may be adapted tooverflow the liquid reservoir 82 and be supplied to the liquid reservoir81 of the first-stage water washing section 64.

As described in detail above, according to the present embodiment, thewater washing section has the two-stage structure, i.e., the first-stagewater washing section 64 and the second-stage water washing section 65,whereby the decarbonated exhaust gas is subjected to amine recovery inthe first-stage water washing section 64, and then further subjected toamine recovery in the second-stage water washing section 65 as well.Thus, the amine compound accompanying the decarbonated exhaust gas canbe recovered very efficiently, and the operating cost can be reduced.

Additionally, if the water washing section remains a one-stage structureand is given a large height only, recovery performance for the aminecompound improves. However, the amine concentration in the washing waterin the water washing section becomes so high that the amineconcentration in the decarbonated exhaust gas cannot be madesufficiently low because of vapor-liquid equilibrium. These facts showthat constructing the water washing section in the two-stage form is avery effective means.

According to the present embodiment, moreover, washing water in thesecond-stage water washing section 65 is withdrawn and supplied to thefirst-stage water washing section 64, whereby the concentration of aminecontained in the washing water in the first-stage water washing section64 is decreased to enhance the amine recovery ability in the first-stagewater washing section 64. In accordance with this advantage, theconcentration of amine contained in the washing water in thesecond-stage water washing section 65 is further decreased to furtherenhance the amine recovery ability as a whole.

According to the present embodiment, moreover, regeneration towerrefluxed water is supplied, as washing water, to the second-stage waterwashing section 65, whereby the concentration of amine contained in thewashing water in the second-stage water washing section 65 is furtherdecreased to further enhance the amine recovery ability in thesecond-stage water washing section 65. Furthermore, washing water in thesecond-stage water washing section 65 is withdrawn and supplied to thefirst-stage water washing section 64, whereby the concentration of aminecontained in the washing water in the first-stage water washing section64 is decreased to enhance the amine recovery ability in the first-stagewater washing section 64.

It is desirable that as described above, regeneration tower refluxedwater is supplied to the second-stage water washing section 65, andwashing water in the second-stage water washing section 65 is withdrawnand supplied to the first-stage water washing section 64. However, thismode is not necessarily restrictive. Instead, regeneration towerrefluxed water may be supplied to the second-stage water washing section65 and the first-stage water washing section 64 at the same time.

According to the present embodiment, moreover, the demisters 83, 84 and85 are installed at the outlets of the carbon dioxide absorption section73, first-stage water washing section 64 and second-stage water washingsection 65. This means can prevent the situation that part of theabsorbing solution mist fed to the carbon dioxide absorption section 73and part of the washing water mist fed to each of the first-stage waterwashing section 64 and the second-stage water washing section 65 arereleased to the outside of the absorption tower together with thedecarbonated exhaust gas, causing losses in water and amine compound.

The decarbonation apparatus equipped with the amine recovery apparatusdescribed above is an apparatus with a high ability to recover the aminecompound and involving a low operating cost.

The first-stage water washing section 64 and the second-stage waterwashing section 65 may be in a packed tower or in a tower with trays.

In the above embodiment, the water washing section is formed as thetwo-stage structure. However, this is not necessarily restrictive, andthe water washing section may have a structure comprising a plurality ofstages not less than three stages. In this case as well, thedecarbonated exhaust gas containing an amine compound is subjected toamine recovery in the water washing section at a preceding stage (astage upstream from a decarbonated exhaust gas flow), and then isfurther subjected to amine recovery in the water washing section at asucceeding stage (a stage downstream from the decarbonated exhaust gasflow). That is, recovery of the amine compound accompanying thedecarbonated exhaust gas is performed sequentially in plural stages ofwater washing sections. In this case, the regeneration tower ref luxedwithdrawn water may be supplied to the water washing section in therearmost stage among the plural-stage water washing sections, andwashing water may be withdrawn from the rearmost-stage water washingsection and supplied to the water washing section in the stage precedingit, further withdrawn from the water washing section in this stage andsupplied to the water washing section preceding to it, and so on.

In the above embodiment, absorption of carbon dioxide contained in thecombustion exhaust gas of fuel is taken as an example for explanation.However, this is not restrictive, and the carbon dioxide-containing gasto be decarbonated may be a process gas such as a fuel gas, and othervarious gases can be applied. The pressure of the carbondioxide-containing gas to be decarbonated may be an applied pressure oran atmospheric pressure, and its temperature may be a low temperature ora high temperature, without any restrictions. The combustion exhaust gasat atmospheric pressure is preferred.

[Explanation for Concrete Experiment Examples]

The present invention will be described concretely by an experimentalexample, which in no way limit the present invention.

<Experimental Example>

The following experiments were conducted as the method of the presentinvention: 30 Nm³/h of a combustion exhaust gas containing 10% carbondioxide was supplied to the carbon dioxide absorption section 73 of theabsorption tower 61, and brought into countercurrent contact with anaqueous solution of an alcoholic hydroxyl group-containing secondaryamine (i.e., an absorbing solution) to absorb carbon dioxide to theaqueous solution. The residual decarbonated exhaust gas was fed to thedemister 83 at the outlet of the carbon dioxide absorption section, thenbrought into countercurrent contact with washing water at a liquid/gasratio of 2.2 l/Nm³ in the first-stage water washing section 64, andpassed through the demister 84 at the outlet of the first-stage waterwashing section. Further, the decarbonated exhaust gas was brought intocountercurrent contact with washing water at a liquid/gas ratio of 2.2l/Nm³ in the second-stage water washing section 65, passed through thedemister 85 at the outlet of the second-stage water washing section, andreleased to the outside of the system. During this procedure, theoperation was performed such that the temperature of the gas at theoutlet of the first-stage water washing section and the temperature ofthe gas at the outlet of the second-stage water washing section wereboth 46° C. Also, regeneration tower ref luxed withdrawn water was fedat 1.1 l/h to the second-stage water washing section 65, while washingwater of the second-stage water washing section 65 was withdrawn andsupplied to the first-stage water washing section 64. As a result, theamine concentration in the decarbonated exhaust gas released from theabsorption tower 61 to the outside of the system was 8 ppm.

<Comparative Example 1>

The same procedure as in the above experimental example was performed,except that the water washing section was a one-stage structure, and theregeneration tower refluxed withdrawn water was supplied to theone-stage water washing section, as the conventional method. As aresult, the amine concentration in the decarbonated exhaust gas releasedfrom the absorption tower 61 to the outside of the system was 25 ppm, ahigher value than in the above-mentioned Example.

<Comparative Example 2>

The same procedure as in the above experimental example was performed,except that the liquid withdrawn from the second-stage water washingsection (washing water) was not supplied to the first-stage waterwashing section 64. As a result, the amine concentration in thedecarbonated exhaust gas released from the absorption tower to theoutside of the system was 11 ppm. This value was sufficiently lowcompared with the above Comparative Example 1, but was higher than inthe above-mentioned experimental example. These findings were able toconfirm the effectiveness of withdrawing washing water of thesecond-stage water washing section 65 and supplying it to thefirst-stage water washing section 64.

The results of the Experimental Example and Comparative Examples 1 and 2are summarized in [Table 1]. By constituting the water washing sectioninto the two-stage structure, the concentration of amine released to theoutside of the system can be made sufficiently low. Also, washing waterof the second-stage water washing section 65 is withdrawn and suppliedto the first-stage water washing section 64, whereby the concentrationof amine released to the outside of the system can be made even lower.

TABLE 1 Exp. Comp. Comp. Ex. 1 Ex. 1 Ex. 2 First-stage water washingsection 2.2 2.2 2.2 liquid/gas ratio (1/Nm³) First-stage water washingsection 46 46 46 outlet gas temperature (° C.) Second-stage waterwashing section 2.2 — 2.2 liquid/gas ratio (1/Nm³) Second-stage waterwashing section 46 — 46 outlet gas temperature (° C.) Regeneration towerrefluxed 1.1 1.1 1.1 withdrawn water flow rate (1/h) Supply ofsecond-stage water washing Yes — No section withdrawn liquid to first-stage water washing section Amine concentration of carbon 8 25 11dioxide absorption tower outlet gas (ppm)

Industrial Applicability

As described above, the present invention relates to an amine recoverymethod and apparatus, and a decarbonation apparatus equipped with theamine recovery apparatus. This invention is useful when applied torecovering an amine compound accompanying a decarbonated exhaust gas ina decarbonation process in which carbon dioxide is removed from a gascontaining carbon dioxide with the use of an amine compound-containingabsorbing solution.

What is claimed is:
 1. An amine recovery method for recovering an aminecompound accompanying a decarbonated exhaust gas formed by removingcarbon dioxide from an exhaust gas by vapor-liquid contact with anabsorbing solution containing the amine compound in a carbon dioxideabsorption section, comprising bringing the decarbonated exhaust gasinto vapor-liquid contact with washing water in a water washing sectionwherein said bringing includes performing said bringing in a pluralityof stages and diluting the washing water before supplying to each of theplurality of stages where the amine compound accompanying thedecarbonated exhaust gas is sequentially recovered.
 2. The aminerecovery method of claim 1, wherein said bringing includes supplyingregeneration tower refluxed water as the washing water to the waterwashing section.
 3. The amine recovery method of claim 1, wherein saiddiluting includes withdrawing the washing water from the water washingsection in one of the plurality of stages and supplying the washingwater to the water washing section in a stage preceding said one of theplurality of stages.
 4. The amine recovery method of claim 1, furthercomprising providing demisters at outlets of the carbon dioxideabsorption section and the water washing section in each of theplurality of stages, said demisters being configured to remove anabsorbing solution mist and a washing water mist accompanying thedecarbonated exhaust gas.
 5. The amine recovery method of claim 2,wherein said diluting includes withdrawing washing water from the waterwashing section in one of the plurality of stages and supplying thewashing water to the water washing section in a stage preceding said oneof the plurality of stages.
 6. The amine recovery method of claim 2,further comprising providing demisters at outlets of the carbon dioxideabsorption section and the water washing section in each of theplurality of stages, said demisters being configured to remove anabsorbing solution mist and a washing water mist accompanying thedecarbonated exhaust gas.
 7. The amine recovery method of claim 3,further comprising providing demisters at outlets of the carbon dioxideabsorption section and the water washing section in each of theplurality of stages, said demisters being configured to remove anabsorbing solution mist and a washing water mist accompanying thedecarbonated exhaust gas.